U.S. patent application number 12/573379 was filed with the patent office on 2010-04-15 for organic el display apparatus.
This patent application is currently assigned to CANON KABUSHIKI KAISHA. Invention is credited to Kenichi Ikari, Toshifumi Mori, Satoru Shiobara, Koichi Suzuki, Akira Tsuboyama.
Application Number | 20100090209 12/573379 |
Document ID | / |
Family ID | 41571466 |
Filed Date | 2010-04-15 |
United States Patent
Application |
20100090209 |
Kind Code |
A1 |
Ikari; Kenichi ; et
al. |
April 15, 2010 |
ORGANIC EL DISPLAY APPARATUS
Abstract
Provided is an organic EL display apparatus which can be driven
at a low voltage and in which a red-light-emitting device uses a
phosphorescent material, a green-light-emitting device uses a
delayed fluorescent material, and the same material is used in the
hole transport layers of the respective devices.
Inventors: |
Ikari; Kenichi;
(Kawasaki-shi, JP) ; Tsuboyama; Akira;
(Machida-shi, JP) ; Suzuki; Koichi; (Yokohama-shi,
JP) ; Shiobara; Satoru; (Kawasaki-shi, JP) ;
Mori; Toshifumi; (Tokyo, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
1290 Avenue of the Americas
NEW YORK
NY
10104-3800
US
|
Assignee: |
CANON KABUSHIKI KAISHA
Tokyo
JP
|
Family ID: |
41571466 |
Appl. No.: |
12/573379 |
Filed: |
October 5, 2009 |
Current U.S.
Class: |
257/40 ;
257/E51.022; 257/E51.026 |
Current CPC
Class: |
H01L 51/5016 20130101;
H01L 27/3211 20130101; H01L 51/5048 20130101 |
Class at
Publication: |
257/40 ;
257/E51.022; 257/E51.026 |
International
Class: |
H01L 51/52 20060101
H01L051/52; H01L 51/54 20060101 H01L051/54 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 10, 2008 |
JP |
2008-264192 |
Sep 24, 2009 |
JP |
2009-219064 |
Claims
1. An organic EL display apparatus, comprising: an organic EL
device that emits red light as a first pixel; an organic EL device
that emits green light as a second pixel; and an organic EL device
that emits blue light as a third pixel, wherein: the organic EL
device that emits red light comprises a host material and a
phosphorescent material as a guest material in its light-emitting
layer; the organic EL device that emits green light comprises a
host material and a delayed fluorescent material as a guest
material in its light-emitting layer; and a hole transport layer of
the organic EL device that emits red light and a hole transport
layer of the organic EL device that emits green light comprise the
same material.
2. The organic EL display apparatus according to claim 1, wherein
the hole transport layer of the organic EL device that emits red
light and the hole transport layer of the organic EL device that
emits green light are continuously disposed.
3. The organic EL display apparatus according to claim 2, wherein
the delayed fluorescent material comprises one of compounds
represented by the following structural formulae: ##STR00010##
4. The organic EL display apparatus according to claim 3, wherein
the phosphorescent material comprises a compound represented by the
following structural formula: ##STR00011##
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an organic EL display
apparatus, and more specifically, to an organic EL display
apparatus using an organic EL device having a delayed fluorescent
material as a pixel.
[0003] 2. Description of the Related Art
[0004] In recent years, researches have been vigorously conducted
on organic EL display apparatuses each using an organic EL
device.
[0005] A light-emitting material for use in the organic EL device
includes, for example, a fluorescent material and a phosphorescent
material.
[0006] In addition, Japanese Patent Application Laid-Open No.
2004-241374 describes that a delayed fluorescent material is used
in an organic EL device for improving the emission efficiency.
Japanese Patent Application Laid-Open No. 2004-241374 describes
that the delayed fluorescent material showed each of a strong
delayed fluorescent spectrum and a strong phosphorescent spectrum
within the range of 520 nm to 750 nm.
SUMMARY OF THE INVENTION
[0007] Use of a phosphorescent material enables a red color organic
EL device to emit light with high efficiency. However, a green
color organic EL device or blue color organic EL device is
susceptible to improvement in order that the device may be able to
emit light with high efficiency.
[0008] A phosphorescent material can be theoretically expected to
emit light with higher efficiency than a fluorescent material does.
However, even the phosphorescent material is still susceptible to
improvement in terms of green or blue light emission.
[0009] Japanese Patent Application Laid-Open No. 2004-241374
describes that the delayed fluorescent material described in the
document showed each of a strong delayed fluorescent spectrum and a
strong phosphorescent spectrum in the range of 520 nm to 750 nm.
However, an emission wavelength actually illustrated in a figure is
formed of a peak having a maximum emission wavelength in excess of
550 nm and a peak having a maximum emission wavelength in excess of
600 nm. That is, the delayed fluorescent material is not a
light-emitting material capable of emitting light of a primary
color such as a green or blue color in terms of its color
purity.
[0010] The present invention provides an organic EL display
apparatus excellent in power consumption and capable of emitting
lights of three colors, i.e., red, green, and blue colors by making
contrivance to a green color organic EL device which is susceptible
to improvement in terms of its emission efficiency.
[0011] That is, the present invention provides an organic EL
display apparatus including: an organic EL device that emits red
light as a first pixel; an organic EL device that emits green light
as a second pixel; and an organic EL device that emits blue light
as a third pixel, in which: the organic EL device that emits red
light includes a phosphorescent material in its light-emitting
layer; the organic EL device that emits green light has a delayed
fluorescent material in its light-emitting layer; and a hole
transport layer of the organic EL device that emits red light and a
hole transport layer of the organic EL device that emits green
light include the same material.
[0012] According to the present invention, there can be provided an
organic EL display apparatus that shows a small power consumption
by using a delayed fluorescent material in an organic EL device
that emits green light.
[0013] Further features of the present invention will become
apparent from the following description of exemplary embodiments
with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a schematic diagram illustrating an emission
process for phosphorescence.
[0015] FIG. 2 is a schematic diagram illustrating an emission
process for delayed fluorescence.
DESCRIPTION OF THE EMBODIMENTS
[0016] The organic EL display apparatus according to the present
invention is an organic EL display apparatus including: an organic
EL device that emits red light as a pixel; an organic EL device
that emits green light as a pixel; and an organic EL device that
emits blue light as a pixel, in which: the organic EL device that
emits red light includes a host material and a phosphorescent
material as a guest material in its light-emitting layer; the
organic EL device that emits green light includes a host material
and a delayed fluorescent material as a guest material in its
light-emitting layer; and the hole transport layer of the organic
EL device that emits red light and the hole transport layer of the
organic EL device that emits green light include the same
material.
[0017] The organic EL device that emits red light causes the
phosphorescent material to emit light. This is because the
phosphorescent material emits light with high efficiency. Since the
energy of red light emission is smaller than the energy of the
emission of light of any other color, the S1 excited state of the
host material that supplies its excitation energy to the
phosphorescent material via the T1 excited states of the materials
is not required to be high. The foregoing means that neither the
expansion of the band gap of the host material nor the deepening
(distancing from a vacuum level) of the HOMO of the host material
is needed.
[0018] The term "T1 excited state" herein employed refers to the
lowest excited triplet state. The term "host material" herein
employed refers to a material which constitutes the light-emitting
layer and has a higher weight ratio than that of the guest
material. The term "guest material" herein employed refers to a
material which constitutes the light-emitting layer.
[0019] On the other hand, when a phosphorescent material is used in
the organic EL device that emits green light, higher energy than
the energy of the red light is needed.
[0020] As a result, the S1 excited state of the host material needs
to be raised.
[0021] Of course, the organic EL device that emits red light and
the organic EL device that emits green light are different from
each other in emission color; a difference in band gap or HOMO
between the host materials of both the devices is preferably as
small as possible from the viewpoint of a reduction in the drive
voltage of the display apparatus.
[0022] In view of the foregoing, in the present invention, the
delayed fluorescent material is used as a guest material for the
organic EL device that emits green light.
[0023] A fluorescent material that is not a delayed fluorescent
material theoretically has lower efficiency than that of a
phosphorescent material. However, since the fluorescent material
emits light in its S1 excited state, i.e., its lowest excited
singlet state, the S1 excited state of a host material can be made
lower than the S1 excited state of a host material to be used when
the phosphorescent material is used. That is, the fluorescent
material has the potential to allow an organic EL device to be
driven at a low voltage.
[0024] In the present invention, attention was paid to the delayed
fluorescent material as a material capable of emitting light with
high efficiency while being a fluorescent material.
[0025] That is, now that a phosphorescent material capable of
emitting light with high efficiency is adopted for the red color
and hence low voltage driving can be achieved for the organic EL
device that emits red light, low voltage driving must also be
achieved for an organic EL device that emits light of any other
color, specifically green light. In view of the foregoing, in the
present invention, the phosphorescent material has been used in the
organic EL device that emits red light, and the delayed fluorescent
material has been used in the organic EL device that emits green
light.
[0026] With such procedure, there arises no difference in band gap
or HOMO between the host materials of the organic EL devices for
the both colors, so that the hole transport layers of the
respective organic EL devices can be formed of the same
material.
[0027] The term "hole transport layer" refers to a layer that is
adjacent to the light-emitting layer and is provided on a side
close to an anode.
[0028] The term "organic EL device" refers to a device having at
least a pair of electrodes and organic compound layers interposed
between the electrodes.
[0029] The organic compound layers of each organic EL device
according to the present invention have at least a light-emitting
layer and a hole transport layer. The organic compound layers may
appropriately have a hole injection layer, an electron blocking
layer, a hole blocking layer, an electron transport layer, or an
electron injection layer in addition to the above layers.
[0030] The term "pair of electrodes" refers to an anode and a
cathode. In the organic EL display apparatus according to the
present invention, which has a plurality of organic EL devices, the
electrodes on one side of the respective organic EL devices may be
common, that is, may be made conductive with each other. That is,
for example, a constitution can be adopted in which a cathode is
provided in common to the multiple organic EL devices, and anodes
are independently provided for the respective organic EL
devices.
[0031] Examples of the delayed fluorescent material used in the
present invention include a copper complex, a platinum complex, and
a palladium complex. Examples of the delayed fluorescent materials,
Chem 1 and Chem 2, are shown below.
##STR00001##
[0032] The term "delayed fluorescence" herein employed refers to
thermal excitation-type delayed fluorescence.
[0033] The thermal excitation-type delayed fluorescence is as
follows: an exciton in its lowest excited triplet state absorbs
thermal energy to be thermally excited to its lowest excited
singlet state, and then the exciton emits light from its lowest
excited singlet state.
[0034] When the delayed fluorescent material is used in an organic
EL device, an exciton in a triplet state as well as an exciton in a
25% singlet state produced by carrier recombination undergoes
intersystem crossing toward a singlet state.
[0035] Accordingly, in principle, an emission yield of 100% can be
expected from the device.
[0036] Here, the emission mechanisms for the delayed fluorescence
and phosphorescence are compared with each other with reference to
FIGS. 1 and 2.
[0037] First, reference numerals in the figures are described.
Reference numeral 101 denotes S1 energy; 102, a lowest excited
singlet state; 103, intersystem crossing; 104, a lowest excited
triplet state; 105, light emission; 106, T1 energy; 107, a ground
state; 201, S1 energy; 202, a lowest excited singlet state; 203,
intersystem crossing; 204, a lowest excited triplet state; 205,
light emission; and 206, T1 energy.
[0038] FIG. 1 is a diagram schematically illustrating the emission
mechanism for phosphorescence. Of a singlet exciton in the lowest
excited singlet state 102 produced by carrier recombination and a
triplet exciton in the lowest excited triplet state 104, the
singlet exciton undergoes the intersystem crossing 103 to be turned
into the triplet exciton, and the triplet exciton undergoes a
transition to the ground state 107, so that the light emission 105
occurs.
[0039] FIG. 2 is a diagram schematically illustrating the emission
mechanism for the delayed fluorescence. Of a singlet exciton in the
lowest excited singlet state 202 produced by carrier recombination
and a triplet exciton in the lowest excited triplet state 204, the
triplet exciton undergoes the intersystem crossing 203 to be turned
into the singlet exciton, and the singlet exciton undergoes a
transition to the ground state 207, so that the light emission 205
occurs.
[0040] Phosphorescence and the delayed fluorescence are compared
with each other with reference to FIGS. 1 and 2. The length in the
vertical direction of each figure is defined as the magnitude of
energy, and it is assumed that light having the same wavelength is
emitted in both the phosphorescence and the delayed fluorescence.
It can be found by paying attention to an energy difference between
the singlet exciton and the ground state (S1 energy 101 or 201) and
an energy difference between the triplet exciton and the ground
state (T1 energy 106 or 206) that each of the S1 energy and T1
energy of the delayed fluorescence is smaller than the
corresponding one of phosphorescence (101<201 and 106<206).
That is, an energy difference (energy gap) between an excited state
and a ground state in the delayed fluorescence is smaller than that
in phosphorescence at the same emission wavelength.
[0041] When the energy gap of a light-emitting material, i.e., a
guest material in an organic EL device is small, the energy gap of
a host material may be small. Accordingly, an energy difference
between the energy gap and the work function of an electrode for
use in an anode or cathode, the HOMO of a hole transport layer, or
the LUMO of an electron transport layer becomes small, so that an
injection barrier for a hole and an injection barrier for an
electron become small. As a result, the drive voltage of the
organic EL device is reduced. Therefore, each of the S1 energy and
T1 energy of the delayed fluorescent material is smaller than the
corresponding one of a phosphorescent material at the same emission
wavelength, so that an injection barrier for a hole and an
injection barrier for an electron become small, and hence the drive
voltage of the organic EL device is reduced.
[0042] The delayed fluorescent material satisfies all of the
following properties:
(1) the emission lifetime at room temperature (298 K) is at a level
of microsecond; (2) the emission wavelength at room temperature
(298 K) is shorter than an emission wavelength at a low temperature
(77 K); (3) the emission lifetime at room temperature (298 K) is
much shorter than an emission lifetime at the low temperature (77
K); and (4) the emission intensity increases with increasing
temperature.
[0043] In the case of fluorescence which is not the delayed
fluorescence or phosphorescence, comparison between an emission
wavelength at room temperature and an emission wavelength at a low
temperature shows that the wavelengths are identical to each other,
or the emission wavelength at the low temperature is shorter than
the other. In contrast, in the case of the delayed fluorescence, an
emission wavelength at the low temperature is longer than an
emission wavelength at room temperature. This is because of the
following reason: although light emission from a singlet is
observed at room temperature, light emission occurs at the low
temperature from the energy level of a triplet which is lower than
that of the singlet. The term "emission wavelength" herein employed
refers to the maximum emission wavelength or the emission start
wavelength.
[0044] In addition, in the case of fluorescence which is not the
delayed fluorescence, the emission lifetime is at a level of
nanosecond because light emission occurs from a singlet. In the
case of phosphorescence in which a triplet is involved in light
emission, the emission lifetime is at a level of microsecond. In
the case of the delayed fluorescence, the emission lifetime is at a
level of microsecond because a triplet is involved in light
emission. The delayed fluorescent material used in the present
invention has an emission lifetime of 0.1 microsecond or more and
less than 1 millisecond in a solid state or solution state.
[0045] With regard to the emission lifetime, the emission lifetime
of each of the delayed fluorescence and phosphorescence is at a
level of microsecond; in the case of the delayed fluorescence,
however, the emission lifetime at a low temperature is much longer
than the emission lifetime at room temperature. For example, when
it is assumed that non-radiation deactivation is suppressed at a
low temperature, in the case of a phosphorescent material having a
quantum yield at room temperature of 0.1, the emission lifetime at
the low temperature is at most ten times the emission lifetime at
room temperature. In the case of the delayed fluorescent material,
the emission lifetime strongly depends on temperatures because
light emission occurs from different excited states at the low
temperature and room temperature. Light emission occurs from a
singlet at room temperature while light emission occurs from a
triplet at the low temperature. Accordingly, the emission lifetime
of the delayed fluorescent material at the low temperature is ten
or more times the emission lifetime of the material at room
temperature; depending on the kind of the material, it may be
observed that the former is two or more orders of magnitude longer
than the latter. The emission lifetime of the delayed fluorescent
material used in the present invention shows the following
characteristic when the material is in a solid state or solution
state: an emission lifetime at the low temperature is 10 or more
times, more specifically 50 or more times, or still more
specifically 100 or more times the emission lifetime at room
temperature.
[0046] In the case of phosphorescence, a non-radiation deactivation
rate increases with increasing temperature, so that the emission
intensity reduces. In contrast, in the case of the delayed
fluorescence, the emission intensity increases with increasing
temperature. This is because of the following reason: the
probability in which intersystem crossing from a triplet to a
singlet occurs increases by virtue of external temperature energy,
so that a triplet exciton undergoes intersystem crossing to a
singlet so as to be capable of easily emitting light.
[0047] The organic EL display apparatus according to the present
invention has each of red (R), green (G), and blue (B) pixels
placed in its plane. Each pixel has an organic EL device. The
respective pixels are connected with one another through a data
signal line for each pixel column, or are connected with one
another through a scanning signal line for each pixel row.
[0048] Each pixel is connected to an organic EL device and to a TFT
for controlling the luminance of the organic EL device.
[0049] The direction in which light is extracted may be of a bottom
emission type in which light is extracted through a substrate
having an organic EL device in its plane, or may be of a top
emission type in which light is extracted not via a substrate.
[0050] The organic EL display apparatus according to the present
invention is applicable to any embodiment with no limitation as
long as the display apparatus is used in, for example, a display
apparatus for a television or personal computer, or an instrument
having a unit for displaying an image. For example, a portable
display apparatus on which the display apparatus of the present
invention is mounted is available. Alternatively, the display
apparatus of the present invention can be used in the display unit
of an electronic imaging device such as a digital camera or of a
mobile phone.
[0051] In the present embodiment, the host material for the
light-emitting layer may be, for example, CBP shown below (Chem
3).
[0052] The hole transport layer can be formed of, for example, PF01
shown below (Chem 4) having electron-donating property. The
electron transport layer can be formed of, for example, Bphen shown
below (Chem 5) having electron-accepting property.
[0053] In the present invention, the hole transport layer of the R
pixel and the hole transport layer of the G pixel, which are formed
using the same material, are preferably a common layer continuously
formed extending over the R pixel and the G pixel.
##STR00002##
[0054] A fluorescent material rather than a phosphorescent material
is preferably used as a guest for the light-emitting layer of the
organic EL device that emits blue light from the viewpoint of a
reduction in the drive voltage of the display apparatus.
EXAMPLES
Green Color Organic EL Device 1
[0055] A green color organic EL device 1 having the following
constitution was produced.
[0056] Materials for, and the thicknesses of, the respective
layers, and the order in which the layers are stacked are shown
below.
[0057] ITO/PF01 (40 nm)/CBP (host material)+guest material (20
nm)/Bphen (50 nm)/KF (1 nm)/Al (100 nm)
[0058] An ITO film (120 nm) was formed on a non-alkali glass
substrate having a thickness of 1.1 mm by a sputtering process, and
the resultant was used as an anode side transparent electrode. PF01
shown in Chem 4 was formed into a film having a thickness of 40 nm
to serve as a hole transport layer on the electrode by a vacuum
evaporation process at a degree of vacuum of 3.0.times.10.sup.-5
Pa. Next, CBP shown in Chem 3 as a host material and the delayed
fluorescent material shown in Chem 1 as a guest material were
formed into a light-emitting layer having a thickness of 20 nm by a
co-evaporation process under the following conditions: a ratio
(concentration) of the guest material to the host material of 5 vol
% and a degree of vacuum of 3.0.times.10.sup.-5 Pa.
[0059] Next, bathophenanthroline (Bphen) shown in Chem 5 was formed
into a film having a thickness of 50 nm to serve as an electron
transport layer by a vacuum evaporation process at a degree of
vacuum of 3.0.times.10.sup.-5 Pa. Next, potassium fluoride (KF) was
formed into a film having a thickness of 1 nm to serve as an
electron injection layer by a vacuum evaporation process at a
degree of vacuum of 2.0.times.10.sup.-4 Pa. Finally, Al as a
cathode material was formed into a film having a thickness of 100
nm by a vacuum evaporation process at a degree of vacuum of
2.0.times.10.sup.-4 Pa. Thus, the organic EL device was
obtained.
[0060] The organic EL device was evaluated by the following
methods. A DC constant-current power source (manufactured by ADC
CORPORATION, trade name: R6243) was used as a driving power source.
A luminance meter (manufactured by TOPCON CORPORATION, trade name:
BM-7 FAST) was used in luminance measurement. An instantaneous
multi-photometric system (MCPD-7000 (trade name); manufactured by
OTSUKA ELECTRONICS CO., LTD.) was used in CIE chromaticity
measurement. The organic EL device produced in this example was
evaluated for its values of CIE chromaticity, drive voltage, and
emission efficiency at a luminance of 100 cd/m.sup.2.
[0061] When the organic EL device produced in this example was
caused to emit light at a luminance of 100 cd/m.sup.2, the device
emitted green light having CIE chromaticity coordinates of (0.33,
0.65). At that time, the device was driven at a voltage of 4.5 V,
and the device showed an emission efficiency of 24 cd/A.
[0062] (Green Color Organic EL Device 2)
[0063] In this example, an organic EL device was produced and
evaluated by following the same procedure as in the green color
organic EL device 1 with the exception that a delayed fluorescent
material shown in Chem 6 below was used as a guest material in
formation of the light-emitting layer in the green color organic EL
device 1.
##STR00003##
[0064] When the organic EL device produced in this example was
caused to emit light at a luminance of 100 cd/m.sup.2, the device
emitted green light having CIE chromaticity coordinates of (0.32,
0.64). At that time, the device was driven at a voltage of 4.7 V,
and the device showed an emission efficiency of 22 cd/A.
[0065] (Green Color Organic EL Device 3)
[0066] In this example, an organic EL device was produced and
evaluated by following the same procedure as in the green color
organic EL device 1 with the exception that a delayed fluorescent
material shown in Chem 7 below was used as a guest material in
formation of the light-emitting layer in the green color organic EL
device 1.
##STR00004##
[0067] When the organic EL device produced in this example was
caused to emit light at a luminance of 100 cd/m.sup.2, the device
emitted green light having CIE chromaticity coordinates of (0.32,
0.65). At that time, the device was driven at a voltage of 4.8 V,
and the device showed an emission efficiency of 21 cd/A.
[0068] (Green Color Organic EL Device 4)
[0069] In this example, an organic EL device was produced and
evaluated by following the same procedure as in the green color
organic EL device 1 with the exception that the delayed fluorescent
material shown in Chem 2 above was used as a guest material in
formation of the light-emitting layer in the green color organic EL
device 1.
[0070] When the organic EL device produced in this example was
caused to emit light at a luminance of 100 cd/m.sup.2, the device
emitted green light having CIE chromaticity coordinates of (0.33,
0.63). At that time, the device was driven at a voltage of 5 V, and
the device showed an emission efficiency of 22 cd/A.
[0071] (Green Color Organic EL Device 5)
[0072] In this example, an organic EL device was produced and
evaluated by following the same procedure as in the green color
organic EL device 1 with the exception that a delayed fluorescent
material shown in Chem 8 below was used as a guest material in
formation of the light-emitting layer in the green color organic EL
device 1.
##STR00005##
[0073] When the organic EL device produced in this example was
caused to emit light at a luminance of 100 cd/m.sup.2, the device
emitted green light having CIE chromaticity coordinates of (0.34,
0.64). At that time, the device was driven at a voltage of 5.2 V,
and the device showed an emission efficiency of 18 cd/A.
[0074] (Green Color Organic EL Device 6)
[0075] In this example, an organic EL device was produced and
evaluated by following the same procedure as in the green color
organic EL device 1 with the exception that a delayed fluorescent
material shown in Chem 9 below was used as a guest material in
formation of the light-emitting layer in the green color organic EL
device 1.
##STR00006##
[0076] When the organic EL device produced in this example was
caused to emit light at a luminance of 100 cd/m.sup.2, the device
emitted green light having CIE chromaticity coordinates of (0.33,
0.65). At that time, the device was driven at a voltage of 5.5 V,
and the device showed an emission efficiency of 19 cd/A.
[0077] (Red Color Organic EL Device 1)
[0078] In this example, an organic EL device was produced and
evaluated by following the same procedure as in the green color
organic EL device 1 with the exception that a phosphorescent
material Ir(piq).sub.3 shown in Chem 10 below was used as a guest
material in formation of the light-emitting layer in the green
color organic EL device 1.
##STR00007##
[0079] When the organic EL device produced in this example was
caused to emit light at a luminance of 100 cd/m.sup.2, the device
emitted red light having CIE chromaticity coordinates of (0.66,
0.33). At that time, the device was driven at a voltage of 4.5 V,
and the device showed an emission efficiency of 12 cd/A.
[0080] (Green Color Organic EL Device 7)
[0081] In this example, which serves as a reference example, an
organic EL device was produced and evaluated by following the same
procedure as in the green color organic EL device 1 with the
exception that a phosphorescent material Ir(ppy).sub.3 shown in
Chem 11 below was used as a guest material in formation of the
light-emitting layer in the green color organic EL device 1.
##STR00008##
[0082] When the organic EL device produced in this example was
caused to emit light at a luminance of 100 cd/m.sup.2, the device
emitted green light having CIE chromaticity coordinates of (0.35,
0.65). At that time, the device was driven at a voltage of 8 V, and
the device showed an emission efficiency of 20 cd/A.
[0083] (Blue Color Organic EL Device 1)
[0084] In this example, an organic EL device was produced and
evaluated by following the same procedure as in the green color
organic EL device 1 with the exception that a fluorescent material
shown in Chem 12 below was used as a guest material in formation of
the light-emitting layer in the green color organic EL device
1.
##STR00009##
[0085] When the organic EL device produced in this example was
caused to emit light at a luminance of 100 cd/m.sup.2, the device
emitted blue light having CIE chromaticity coordinates of (0.15,
0.13). At that time, the device was driven at a voltage of 5 V, and
the device showed an emission efficiency of 2.5 cd/A.
[0086] (Organic EL Display Apparatus 1)
[0087] An organic EL display apparatus formed of three color
pixels, i.e., R, G, and B pixels was produced by the following
method. The display apparatus is of such a constitution that the R,
G, and B pixels are arrayed in a matrix pattern. The display
apparatus has a panel size of inches in width across corners, and
adopts a QVGA in which 240 pixels are arrayed in a longitudinal
direction and 320 pixels are arrayed in a horizontal direction. The
R, G, and B pixels each have an aperture ratio of 30%.
[0088] First, a TFT drive circuit including low-temperature
polysilicon was formed on a glass substrate as a support member,
and a planarizing film including an acrylic resin was formed on the
circuit. ITO was formed and patterned into a transparent conductive
film having a thickness of 120 nm on the film by a sputtering
process. Furthermore, a device separation film was formed by using
an acrylic resin. Thus, an anode side transparent electrode
substrate was produced. The substrate was subjected to ultrasonic
cleaning with isopropyl alcohol and washing with boiled isopropyl
alcohol, and was then dried. After that, the substrate was
subjected to UV/ozone cleaning, and then organic compounds and a
cathode material were formed into films by vacuum evaporation. The
formation of the films of an organic EL device from the organic
compounds and the cathode material by vacuum evaporation was
performed as follows: each R pixel was of the same constitution as
that of the red color organic EL device 1, each G pixel was of the
same constitution as that of the green color organic EL device 1,
and each B pixel was of the same constitution as that of the blue
color organic EL device 1. At the time of the film formation, the
organic EL devices were separately deposited from the vapor onto
the same substrate with a mask corresponding to an emission pattern
so that the R, G, and B pixels might be arrayed in a matrix fashion
in the plane of the substrate. Furthermore, silicon oxynitride was
formed into a film having a thickness of 700 nm to serve as a
protective film. Thus, the organic EL display apparatus was
obtained. A power consumption upon display of a white w NTSC
(0.310, 0.316) on the organic EL display apparatus at 200
cd/m.sup.2 was determined to be 400 mW.
[0089] (Organic EL Display Apparatus 2)
[0090] An organic EL display apparatus was produced by following
the same procedure as in the organic EL display apparatus 1 with
the exception that the formation of the films of an organic EL
device in the organic EL display apparatus 1 was changed such that
each G pixel was of the same constitution as that of the green
color organic EL device 4. A power consumption upon display of a
white w NTSC (0.310, 0.316) on the organic EL display apparatus at
200 cd/m.sup.2 was determined to be 410 mW.
[0091] (Organic EL Display Apparatus 3)
[0092] An organic EL display apparatus formed of three color
pixels, i.e., R, G, and B pixels was produced by the following
method.
[0093] In this example, the constitution of the lower electrode is
different from that of the previous organic EL display apparatus 1.
In addition, the constitution of the display apparatus is different
from that of the previous organic EL display apparatus 1 in that
the hole transport layer is common to the respective colors, that
is, the same material is continuously provided extending over the
pixels. In addition, the thickness of the light-emitting layer for
each color is different from that of the previous organic EL
display apparatus 1. In addition, the constitution of the display
apparatus is different from that of the previous organic EL display
apparatus 1 in that the electron transport layer is common to the
respective colors, that is, the same material is continuously
provided extending over the pixels. In addition, the constitution
of the display apparatus is different from that of the previous
organic EL display apparatus 1 in that the cathode as an upper
electrode is common to the respective colors, that is, the same
material is continuously provided extending over the pixels. The
display apparatus is of the same constitution as that of the
previous organic EL display apparatus 1 except the foregoing.
[0094] PF01 shown in Chem 4 was formed into a film having a
thickness of 24 nm to serve as a hole transport layer by a vacuum
evaporation process at a degree of vacuum of 3.0.times.10.sup.-5
Pa.
[0095] Next, light-emitting layers corresponding to the respective
R, G, and B pixels were separately applied.
[0096] With regard to each R pixel, CBP shown in Chem 3 as a host
material and the phosphorescent material Ir(piq).sub.3 shown in
Chem 10 as a guest material were formed into a light-emitting layer
having a thickness of 100 nm by a co-evaporation process under the
conditions of a ratio (concentration) of the guest material to the
host material of 5 vol % and a degree of vacuum of
3.0.times.10.sup.-5 Pa.
[0097] With regard to each G pixel, CBP shown in Chem 3 as a host
material and the delayed fluorescent material shown in Chem 1 as a
guest material were formed into a light-emitting layer having a
thickness of 65 nm by a co-evaporation process under the conditions
of a ratio (concentration) of the guest material to the host
material of 5 vol % and a degree of vacuum of 3.0.times.10.sup.-5
Pa.
[0098] With regard to each B pixel, CBP shown in Chem 3 as a host
material and the fluorescent material shown in Chem 12 as a guest
material were formed into a light-emitting layer having a thickness
of 40 nm by a co-evaporation process under the conditions of a
ratio (concentration) of the guest material to the host material of
5 vol % and a degree of vacuum of 3.0.times.10.sup.-5 Pa.
[0099] Next, bathophenanthroline (Bphen) shown in Chem 5 was formed
into a film having a thickness of 10 nm to serve as an electron
transport layer by a vacuum evaporation degree at a degree of
vacuum of 3.0.times.10.sup.-5 Pa.
[0100] Furthermore, Bphen and Cs.sub.2CO.sub.3 were formed into a
film having a thickness of 14 nm to serve as an electron transport
layer by co-evaporation (at a weight ratio of 9:1) at a degree of
vacuum of 2.0.times.10.sup.-4 Pa.
[0101] Silver (Ag) was formed into a film having a thickness of 15
nm to serve as the cathode by a vacuum evaporation process at a
degree of vacuum of 2.0.times.10.sup.-4 Pa.
[0102] In this example, the reflection interface is an interface
between the reflective electrode and the transparent conductive
film in the lower electrode, the emission interface is the center
of the light-emitting layer, and the refractive index of the hole
transport layer and the light-emitting layer is 1.5. In view of the
fact that the emission wavelengths of the R, G, and B pixels are
620 nm, 520 nm, and 445 nm, respectively, the thicknesses of the
respective R, G, and B pixels are set such that light beams emitted
from the pixels enhance one another through interference, and hence
the chromaticity of a color displayed on the apparatus by the
pixels and the efficiency with which the apparatus displays the
color are improved.
[0103] A power consumption when displaying a white W.sub.NTSC
(0.310, 0.316) on the organic EL display apparatus at 200
cd/m.sup.2 was determined to be 400 mW.
Comparative Example 1
[0104] An organic EL display apparatus was produced by following
the same procedure as in the organic EL display apparatus 1 with
the exception that the formation of the films of an organic EL
device in the organic EL display apparatus 1 was changed such that
each G pixel was of the same constitution as that of the green
color organic EL device 7. A power consumption when displaying a
white W.sub.NTSC (0.310, 0.316) on the organic EL display apparatus
at 200 cd/m.sup.2 was determined to be 800 mW.
[0105] While the present invention has been described with
reference to exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed exemplary embodiments.
The scope of the following claims is to be accorded the broadest
interpretation so as to encompass all such modifications and
equivalent structures and functions.
[0106] This application claims the benefit of Japanese Patent
Applications No. 2008-264192, filed Oct. 10, 2008, and 2009-219064,
filed Sep. 24, 2009, which are hereby incorporated by reference
herein in their entirety.
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